During this year, 55 experiments of one-stage bilateral lung allotransplantation and 12 experiments of unilateral lung allotransplantation have been added to our long-standing series. Improvements in surgical technique and immunosuppressive therapy resulted in a gratifying survival record, compatible with other vital organ transplantation. Respiratory function of 8 dogs was maintained totally by transplanted allografts ranging from 47 to 396 days. Immunologic studies, such as the leukocyte migration inhibition test and fluorescent antibody technique, scanning electron microscopy and histopathologic studies, on these materials disclosed the organ specific nature of obligatory lung allografts. We are now able to store the lung for 6 hours with subsequent life-sustaining function. In the coming year, we propose to extend these studies as follows: 1. Analysis of ventilation, perfusion, and diffusion capacity of bilateral lung allografts and bilateral lung reimplants in various stages. 2. Bronchial cytology for early detection of allograft rejection. 3. Further improvements in protective measures of cold and warm ischemic injury to the lung.